1. Field of the Invention
The present invention relates to an image forming apparatus such as a digital color copier, a color laser printer, or the like.
2. Description of Related Art
As represented by conventional color copiers or the like, image forming apparatuses are conventionally known in which image forming units of different colors are arranged in tandem, with a transfer belt-serving as an intermediate transfer body.
The image forming apparatus of this type first forms (primary transfer) toner images of different colors on the transfer belt, and then collectively transfers (secondary transfer) the toner images formed on the transfer belt onto paper conveyed through a conveyance path different from a conveyance path of the transfer belt. To obtain favorable transfer quality in such a transfer belt method, it is required to previously make concentration correction or color adjustment of toner images formed on the transfer belt before transferred onto paper. Thus, in opposition to the upstream portion of the secondary transfer part of the transfer belt, an optical sensor for concentration correction or color adjustment is provided (see numeral 32 in FIG. 1).
However, since the optical sensor for concentration correction or color adjustment has a detection surface thereof arranged in opposition to the transfer belt, this detection surface tends to become stained by a toner dropping thereon. This adhering stain raises a risk that the detection accuracy deteriorates with time.
Thus, in conventional practice, in order to maintain favorably detection accuracy, the stain on the detection surface of the optical sensor is removed on a regular or irregular basis manually by the user who wipes it off or automatically by a cleaning member fitted to, for example, a solenoid driven by a motor.
Japanese Patent Application Laid-open No. 2002-31919 refers to an example of an optical sensor for detecting the color concentration of a toner image formed on a photo conductor, and also proposes that the detection surface of the optical sensor be cleaned by swinging a cleaning member in conjunction with open and close operation of a cover of a main body (see FIGS. 3 and 4 in the patent publication described above).
However, cleaning by the user cannot achieve sufficient cleaning performance, or may cause a secondary problem such as optical sensor breakage or the like.
A method using a motor, a solenoid, or the like requires a large-scale system, thus resulting in disadvantages in terms of cost, space, and the like.
The method of operating the cleaning member in conjunction with the open and close operation of the cover of the main body suffers from a problem such as open and close operation failure caused by cover floating. Moreover, if this cover is a conveyance cover for jam processing, the detection surface of the optical sensor is cleaned when paper jam occurs. Thus, the detection surface is never cleaned unless paper jam occurs, thus resulting in a greater risk of detection failure.